I. Scope of Insect Ecology
II. Ecosystem Ecology
A. Ecosystem Complexity
B. The Hierarchy of Subsystems
III. Environmental Change and Disturbance
IV. Ecosystem Approach to Insect Ecology V. Scope of This Book
INSECTS ARE THE DOMINANT GROUP OF ORGANISMS ON EARTH, IN terms of both taxonomic diversity (>50% of all described species) and ecological function (E.Wilson 1992) (Fig. 1.1). Insects represent the vast majority of species in terrestrial and freshwater ecosystems and are important components of near-shore marine ecosystems as well. This diversity of insect species represents an equivalent variety of adaptations to variable environmental conditions. Insects affect other species (including humans) and ecosystem parameters in a variety of ways. The capacity for rapid response to environmental change makes insects useful indicators of change, major engineers and potential regulators of ecosystem conditions, and frequent competitors with human demands for ecosystem resources or vectors of human and animal diseases.
Insects also play critical roles in ecosystem function. They represent important food resources or disease vectors for many other organisms, including humans, and they have the capacity to alter rates and directions of energy and matter fluxes (e.g., as herbivores, pollinators, detritivores, and predators) in ways that potentially affect global processes. In some ecosystems, insects and other arthropods represent the dominant pathways of energy and matter flow, and their biomass may exceed that of the more conspicuous vertebrates (e.g.,Whitford 1986). Some species are capable of removing virtually all vegetation from a site. They affect, and are affected by, environmental issues as diverse as ecosystem health, air and water quality, genetically modified crops, disease epidemiology, frequency and severity of fire and other disturbances, control of invasive exotic species, land use, and climate change. Environmental changes, especially those resulting from anthropogenic activities, affect abundances of many species in ways that alter ecosystem and, perhaps, global processes.
A primary challenge for insect ecologists is to place insect ecology in an ecosystem context that represents insect effects on ecosystem properties, as well
o 400,000 -ffi
°ther. Other ^^invertebrates 123,400 106,300
Viruses and bacteria
Distribution of described species within major taxonomic groups. Species numbers for insects, bacteria, and fungi likely will increase greatly as these groups become better known. Data from E. O.Wilson (1992).
as the diversity of their adaptations and responses to environmental conditions. Until relatively recently, insect ecologists have focused on the evolutionary significance of insect life histories and interactions with other species, especially as pollinators, herbivores, and predators (Price 1997). This focus has yielded much valuable information about the ecology of individual species and species associations and provides the basis for pest management or recovery of threatened and endangered species. However, relatively little attention has been given to the important role of insects as ecosystem engineers, other than to their effects on vegetation (especially commercial crop) or animal (especially human and livestock) dynamics.
Ecosystem ecology has advanced rapidly during the past 50 years. Major strides have been made in understanding how species interactions and environmental conditions affect rates of energy and nutrient fluxes in different types of ecosystems, how these provide free services (such as air and water filtration), and how environmental conditions both affect and reflect community structure (e.g., Costanza et al. 1997, Daily 1997, H. Odum 1996). Interpreting the responses of a diverse community to multiple interacting environmental factors in integrated ecosystems requires new approaches, such as multivariate statistical analysis and modeling (e.g., Gutierrez 1996, Liebhold et al. 1993, Marcot et al. 2001, Parton et al. 1993). Such approaches may involve loss of detail, such as combination of species into phylogenetic or functional groupings. However, an ecosystem approach provides a framework for integrating insect ecology with the changing patterns of ecosystem structure and function and for applying insect ecology to understanding of ecosystem, landscape, and global issues, such as climate change or sustainability of ecosystem resources. Unfortunately, few ecosystem studies have involved insect ecologists and, therefore, have tended to underrepresent insect responses and contributions to ecosystem changes.
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